Various thermoplastic films have been used to package, preserve, and encase food products. Conventional films are composed of, for example, polypropylene and polyethylene. Optional adhesive layers may be used to combine individual film layers.
Bags made from conventional films are often used for hot water cooking applications. For example, rice and pasta are often cooked in “boil-in” bags.
Conventional bags, however, are unsuited for high temperature cooking applications, such as for example cooking poultry or other meats, because they either melt or adhere to the food product retained therein. Materials that are conventionally used to reduce meat adhesion, such as polyethylene, unfortunately have low softening temperatures and low melt temperatures thereby making them poor choices for high temperature cooking applications.
Conventional bags are also typically not durable enough to be used in high pressure meat casing applications where meat is stuffed into a casing. For example, bags used as meat casing require the ability to elongate significantly before breakage occurs.
The heat sealing of conventional cooking bags is typically accomplished by applying sufficient heat and pressure to adjacent film surfaces for a sufficient period of time in order to produce a fusion bond between the adjacent surfaces. However, heat seals are vulnerable to imperfection where the heat necessary to seal the folds of stock will harm the barrier properties of the film by overly thinning the film layer or melting through the film. Imperfect seals are particularly problematic in cooking applications where exposure to elevated temperatures and heat shrinking can further increase the stress imposed on such seals. While mechanical sealing techniques such as those that make use of clips, rings, or other mechanical devices may substituted for heat sealing, mechanical sealing is associated with a number of undesirable effects such as contamination when the sealing device becomes lost in the packaged product or inability to be used with microwave cooking applications where the sealing device is metallic, as is often the case.
Accordingly, film compositions used in high temperature cooking applications, that may be heat sealed without harmfully influencing desired barrier properties, are desired by the packaging industry.